But if she has not been introduced to the rest of the family, the Christmas gathering will be the opportunity to chat to the Princess Royal, the Earl and Countess of Wessex and the Duke of York and his daughters, who are all expected to attend.

Christmas Day walkabout a chance to meet public

The event also usually attracts hundreds of well-wishers who watch the royal party walk from Sandringham House to the nearby St Mary Magdalene Church, and make the return journey after the Christmas Day service is over.

Members of the royal family usually go on an impromptu walkabout, chatting to local residents, and this could be another opportunity for Ms Markle to meet more of the British public.

Prince Harry meeting members of the public as he attended the Christmas Day church service at Sandringham in 2016Credit:
Chris Jackson /Getty

It is thought that William and Kate, who is pregnant with her third child, will not take their children, Prince George and Princess Charlotte, to the Christmas Day church service.

Where will Meghan and Harry stay at Christmas?

There is speculation that Harry and his bride-to-be might stay with the Cambridges at their nearby home, Anmer Hall.

But if they are accommodated by the Queen and Duke of Edinburgh at Sandringham, they will follow a German tradition observed by generations of the royal family.

The Queen shelters from the rain during the Christmas Day church service at Sandringham in 2015 Credit:
Chris Jackson /Getty

Christmas presents are opened on Christmas Eve, rather than Christmas Day, a legacy of the German heritage of the monarchy.

'All the stars were aligned': How the couple met

After announcing their engagement, the couple gave an insight into their 16-month romance in a BBC interview - and described how they met on a blind date set up by a mutual friend.

Ms Markle told how she could not wait to say "yes" to the prince when Harry got down on one knee a few weeks ago as they cooked a roast chicken dinner at his home, Nottingham Cottage at Kensington Palace.

Indicating the depths of his feeling for his bride-to-be, Prince Harry said: "The fact that I fell in love with Meghan so incredibly quickly was sort of confirmation to me that everything, all the stars were aligned, everything was just perfect.

"It was this beautiful woman just sort of literally tripped and fell into my life, I fell into her life."

Full interview: Harry and Meghan reveal engagement joy

A few months into the relationship, Harry said he had to have "some pretty frank conversations" with Meghan about how her life may change when she entered the royal family.

He added: "But I know that at the end of the day she chooses me, and I choose her, and therefore whatever we have to tackle together or individually we'll always be us together as a team, so I think she's capable... she's capable of anything."

The couple disclosed that Ms Markle had met the Queen twice, an individual she described as an "incredible woman".

The former Suits star was also a big hit with the Queen's beloved corgis, with the prince joking: "I've spent the last 33 years being barked at; this one walks in, absolutely nothing..."

Traditions of a Royal Christmas at Sandringham

The traditions and customs followed by the royal family at Christmas are likely to come as a surprise to Meghan Markle.

While most people across the country open their presents on Christmas Day, the royal family still keep to the German practice of opening their gifts on Christmas Eve.

The Queen, the Duke of Edinburgh and other royals usually congregate in the White Drawing Room at Sandringham House the day before Christmas to put the finishing touches to a 20ft (6m) tree cut from the estate.

Presents are placed on a white linen-covered trestle table, with cards marking exactly where the piles of gifts should be put.

Gifts are exchanged on Christmas Eve at Sandringham

And what should Ms Markle buy the woman who is head of state and lives in palaces? Something useful as the Queen apparently likes practical presents, but not overly extravagant ones.

The Duchess of Cambridge revealed that she was left stumped over what to buy the Queen for Christmas.

"I thought 'I'll make her something'. Which could have gone horribly wrong. But I decided to make my granny's recipe of chutney."

Prince Charles and his wife Camilla lead members of the Royal family as they attend the Christmas Day church service last yearCredit:
PHIL NOBLE /Reuters

At 5pm, guests enjoy tea, scones, sandwiches and cakes from sideboards in the Saloon. Afterwards, they dress for dinner, with the table set with the finest china.

Ms Markle will be separated from Harry later in the evening as, sometime after 10pm, on a signal from the Queen, the corgis are led out and the ladies adjourn, leaving the Duke of Edinburgh to serve port or brandy to the men.

On Christmas Day, the royals awake to find stockings filled with small gifts and fruit at the foot of their beds.